Method of generating heat and light



United YStates arent METHD (lll GENERATING HEAT AND LlGli'i Robert S.Bush, Midland, Donald L. Lernen, Freeland,

and Martin A. Molnar, Sanford, Mich., assignors to The Dow ChemicalCompany, Midland, Mich., a corporation of Delaware No Drawing. FiledSept. 2S, 1959, Ser. No. 845,589

6 Claims. (ill. 149--37 The invention relates to a method of generatingheat and light and more particularly relates to an improved ,method ofgenerating heat and light by the combustion of magnesium ormagnesium-base'alloy.

This is a continuation-impart of the copending application Serial No.700,905, led December 5, 1957, now abandoned.

For the purposes of the specification and claims, magnesium andmagnesium-base alloy containing at least 75 percent by weight ofmagnesium are hereinafter referred to as magnesium metal.

'Heretofore in generating heat and light by burning a magnesium metalthe problem has arisen that When a bulky piece of magnesium metal isburned as by igniting an edge or end of it a substantial proportion ofthe metal melts ahead of the flame or 1ourning area and drips oil'. Insome applications in which a magnesium metal is burned to produce lightas in dares or to produce heat as in devices utilizing magnesium metalas a solid fuel, it is important to prevent this dripping of moltenmetal and thus to permit substantially all of the magnesium to burn inplace in the device.

It is accordingly an object of the invention to provide a method ofgenerating heat and light by the combustion of magnesium metal in such amanner that the magnesium metal burns without dripping.

lIt is another object of the invention to provide a method of generatingheat and light using magnesium metal fuel in such a manner that the fuelis efficiently and smoothly consumed upon ignition.

A still further object of this invention is to generate heat and lightin a manner which permits the use of magnesium metal in a form havingsubstantially the maximum amount of magnesium attainable per unitvolume.

The present invention is based upon the discovery that by admixing asuitable proportion of a solid nonmetallic substance having a relativelyhigh melting point or decomposition temperature (that is above 450 F.)with a suitable particulate solid form of magnesium metal and dieexpressing the mixture at a temperature at which the metal particlesundergo a welding together during the die expression but below atemperature at which the occluded nonmetallic solid melts or decomposesa product is obtained which upon being ignited produces heat and lightas it burns, the burning is steady, and the burning product remainssubstantially coherent and does not drip molten magnesium metal.

The action of the admixed nonmetallic substance is not entirelyunderstood but it is believed that it serves both as an insulator anddiluent. As an insulator, it retards the transfer of heat away from theburning surface so that tlame propagation continues steadily from thepoint of ignition without leaving unburncd sections. AS a diluent itmoderates the burning rate so that burning takes place more smoothlywith less sputtering and heat and light are generated in a more uniformmanner, the brightness of the light being substantially that of ordinarymagnesium.

ln contrast upon igniting an article formed of a magnesium metal whichcontains substantially no nonmetallic substance the article burns in amanner which is entirely different and quite undesired for theproduction of heat and light. In this case the heat of combustion isconducted ahead of the flame so efficiently that metal in the combustionzone melts too rapidly to be consumed and drips from the unmelted mass.It is also believed that as another consequence of the eflicient heattransfer away from the combustion site ignition tends to occur atisolated points ahead of the main flame propagation. As a result, themetal between multiple sites where combustion is occurring becomesmolten and drips or sputters from the article sometimes carrying theburning portions from the main mass so that the generation of heat andlight stops.

While a nonmetallic substance which does not form a fluid except at anelevated temperature is generally applicable in pulverulent form forcoextrusion to form the product used in accordance with the invention,an effective product is formed using magnesium oxide, calcium oxide orstrontium oxide. A fluid is meant to include a liquid generated as bymelting and a gas generated as by decomposition.

When even more effective moderation of combustion of the product used inthis invention is desired, the article is advantageously made using acarbonate lof one of the second group metals cadmium or magnesium as thenonmetallic substance. Various carbonates of the aforesaid second groupmetals muy be used in pulverulent form, for example magnesite (MgCOg),nesquehonite hydromagnesite (3l\flgCO3Mg(Ol-l)23H2O), lansfordite(MgCOg-Sl-lg), artinite (MgCO3-Mg(OH)2-3H2O), cadmium carbonate (CdCOg).Af these, the heavy basic carbonate, hydromagnesite, is preferred. Thesematerials are normally in a finely divided state, for example inparticles smaller than about 50 microns. A preferred range of particlesize is from 0.1 to 5 microns.

Upon admixing such a carbonate with particulated magnesium metal and dieexpressing the mixture at a temperature at which the metal particlesundergo a welding together but below a temperature at which thesooccluded carbonate decomposes an article is obtained which upon beingignited expands ahead of the llame, burns steadily, does not drip moltenmagnesium metal and generates heat and light in a uniform manner untilit is consumed. The expansion in the hot zone ahead of the flame occursas the occluded carbonate decomposes so as to produce gas under pressurein the interstices of the particulate die expressed metal, the dieexpressed article swells and its structure becomes cellular. rthecellular material so-obtained during combustion serves effectively toinsulate the remainder of the article being burned so that flamepropagation continues smoothly from the point of the ignition.

The invention then consists of the aforesaid method of generating heatand light which consists of forming and igniting a magnesium metalproduct which does not drip on burning, `the method being herein fullydescribed and particularly pointed out inthe claims.

ln the process of making the article employed in the method of theinvention, the magnesium metal to be coextruded is suitably comminutedas by grinding, filing, shaving, atomizing or other appropriate method.The particular shape of the metal particles does not appear to becritical.

The particulated metal and the pulverulent nonmetallic solid are mixedtogether in suitable proportions whereby to at least partially coat themetal particles with nonmetallic particles which are preferably dustlike and more or less adhere to the metal particles. The amount ofnonmetallic substance to use may range from about 0.5 to 20 percent ofthe weight of the metal, the preferred amount being about 5 percent inthe case of a carbonate of magnesium or l5 percent in the case ofcadmium carbonate. Generally satisfactory results are had with fromabout 2 to 8 percent of magnesium carbonate, for example. Mixing can beeifected in various ways as for example by tumbling the metal andnonmetal particles together in a closed vessel, such as a barrel whichis turned end over end. Mixing in which the particles are tumbled aboutin a vessel revolving a 50 r.p.m. can be accomplished satisfactorily in3 to 4 minutes, but other mixing times may be used.

The mixture iof metal and nonmetallic particles is charged into thecontainer of an extrusion press and die expressed at 4a temperaturesomewhat lower, for example 25 to 350 Fahrenheit degrees lower, thanthat which would be suitable for the extrusion of the metal alone asunderstood in the metal extrusion art. In the case of magnesium-basealloys, for example, the ltemperature of the charge in the container maybe 'as low as 300 F. It is desirable to avoid extrusion temperatures atwhich excessive decomposition or melting of the nonmetallic materialoccurs Yand for this 4reason it is preferable to extrude the charge atas low a temperature as practicable without incurring the use ofexcessive pressures which tend to produce excessive wear on theextrusion dies and other parts of the extrusion apparatus. Satisfactoryextrusion results can be obtained lover a wide range of temperatures, asfor example 300 to 850 F., 450 to 650 being generally suitable. Theextrusion or die expressing operation welds the metal particles to'gether into a rigid body consisting of a matrix of metal in which thenonmetallic particles are dispersed as more or less discrete massesenveloped in the metal.

Reduction during extrusion is preferably 4 to 1. The extruded shape maybe in any desired form obtainable from the die such as `a rod, barribbon, or tube.

In carrying out the method oi' the invention, the extruded metal productmay be mounted, if desired, in a suitable device, such as a are or otherholder. The product is ignited by means of a flame, fuse or thermitinitiator or other suitable heat producing initiator.

Example l More or less spherical particles of ZK60, a magnesiumbasealloy having a nominal composition of 6 percent zinc, 0.6 percentzirconium, the balance magnesium, were mixed with percent by weight ofmagnesium oxide. Mixing was accomplished by tumbling the metal and oxideparticles in a cylindrical one gallon container on a ball mill stand for3 to 4 minutes. The resulting mixture was placed in a horizontal ramextrusion press `and extruded through a 1 inch `diameter die opening ata container temperature of 500 F. and a die temperature of 500 F. A 1inch diameter rod was extruded at a speed of approximately 0.5 foot perminute.

A section of this extrude was mountedl at one end in a clamp and theother end ignited by means of a welding torch. The burning therebyinitiated proceeded steadily to produce heat and light in a uniformmanner without dripping molten metal.

Example Il Particles of magnesium-base alloy ZK60 in the form of lingsand sawdust were mixed with 5 percent by weight of hydromagnesite.Mixing was accomplished by tumbling the metal and carbonate particles ina cylindrical one gallon container on a ball mill stand for 10 to l5minutes. The resulting mixture was charged into the container of ahorizontal ram extrusion press iitted with a die having a yone inchdiameter opening and extruded in the manner described in Example I.

A section Aof the resulting extrude was mounted at one end iny a clamp.The other end was ignited by means of a welding torch. The so-ignitedextrude expanded ahead of the llame. Burning of the extrude proceededsteadily to produce heat and light in a uniform manner without drippingmolten metal.

Example III More 'or less spherical particles of ZK60 magnesiumbasealloy were mixed with 15 percent by Weight of cadmiurn carbonate. Mixingwas `accomplished by tumbling the metal Iand carbonate particles in acylindrical one gallon container on a ball mill stand for 10 to l5minutes. The resulting mixture was charged into the container of ahorizontal ram extrusion press fitted with a die having a one inchdiameter opening and extruded in the manner described in Example I. Asection of the resulting extrude was mounted at one end in ya clamp. Theother end was ignited by means of a welding torch and found to expandahead of the llame. The burning proceeded steadily to produce heat andlight in a uniform manner Without dripping molten' metal.

By way of a comparison more or less spherical particles of ZK60magnesium-base alloy were placed in a horizontal ram extrusion press andextruded through a one inch diameter die Opening at a containertemperature of 550 F. and a die temperature of y600 F. A one inchdiameter rod was extruded at a speed of approximately 0.5 foot perminute.

A section of the resulting extrude was mounted at one end in a clamp.The other end was ignited by means of a welding torch. The so-ignitedextrude produced heat and light in an entirely sporadic manner. Asburning progressed the extrude ignited at many points on its surface andunburned molten metal dripped from the burning extrude.

By way of an additional comparison a portion of more or less sphericalparticles of ZK60 magnesium-base alloy was mixed with 5 percent byweight of hydromagnesite based on the weight of the metal particles.Mixing was accomplished by tumbling the metal and hydromagnesiteparticles together in a cylindrical one gallon container on a ball millstand for about an hour. A 1250 gram charge of the resulting mixture wasplaced in a horizontal ram extrusion press having a 4 inch diametercontainer. The die opening of the press was blocked olf. The containerand die were maintained at a temperature `of about 550 F. while the saidcharge was compressed and held under a compacting pressure of 475 tonsfor 2 minutes. The die was then removed from the press and the compactwas ejected. After it had been allowed to cool the ejected compact wasmachined into the form of a rectangular bar 0.5 inch x 0.5 inch x 3inches. The bar was cantilever supported by means of a clamp in alaboratory hood land ignited at the free end with an acetylene torch.Almost instantaneously the ignited end of the bar exploded showeringburning magnesium metal particles over an area 5 feet in radius andextinguishing or removing all burning metal from the bar. The end of theremaining portion of the bar was again ignited and again the ignited endimmediately exploded, scattering burning magnesium metal particles andextinguishing all burning of the remaining part of the bar held by theclamp.

What is claime-d is:

l. In the heat and light generating combustion of a magnesium metal, theimprovement which consists` in employing as the combustible material, `arigid solid consisting essentially of a physical admixture consisting of0.5 to 2O percent by weight of a particulated substance, the balanceparticulated magnesium metal thereby to avoid dripping molten metalduring combustion, said rigid solid being in the -form of an extrude,and said particulated substance being selected from the group consistingof the oxides, carbonates and basic carbonates of magnesium, calcium,strontium, cadmium.

2. In the heat and light generating combustion of a magnesium metal, theimprovement which consists in employing as the combustible material arigid solid consisting essentially of an intimate admixture consistingof 0.5 to 20 percent by weight of a particulated substance selected fromthe group consisting of oxides, -carbonates and basic carbonates ofmagnesium, cadmium and the alkaline earth metals, the balanceparticulated magnesium metal, said combustible material having the formof an extrude prepared by die expressing said admixture at a temperaturein the range of 300 to 850 F. whereby the magnesium metal particlesundergo a welding together during die eX- pression, but below thetemperature at which the substance forms a uid, thereby to avioddripping molten metal during combustion.

3. The method as in claim 1 in which the particulated substance is abasic carbonate of one of the said magnesium, calcium, strontium,cadmium.

4. The method as in claim 1 in which the particulated substance is `acarbonate of one of the said magnesium, calcium, strontium, cadmium.

5. The method as in claim 4 in which the carbonate is hydromagnesite.

6. The method as in claim 1 in which the substance is an oxide of one ofthe said magnesium, calcium, strontium, cadmium.

References Cited in the le of this patent UNITED STATES PATENTS OTHERREFERENCES Goetzel: Treatise on Powder Metallurgy, volume I, 1949, p.196.

Frazier: Proceedings 14th Annual Meeting, Metal Powder Association,April 21-3, 1958, p. 69.

2. IN THE HEAT AND LIGHT GENERATING COMBUSTION OF A MAGNESIUM METAL, THEIMPROVEMENT WHICH CONSISTS IN EMPOLYING AS THE COMBUSTIBLE MATERIAL ARIGID SOLID CONSISTING ESSENTIALLY OF AN INTIMATE ADMIXTURE CONSISTINGOF 0.5 TO 20 PERCENT BY WEIGHT OF A PARTICULATED SUBSTANCE SELECTED FROMTHE GROUP CONSISTING OF OXIDES, CARBONATES AND BASIC CARBONATES OFMAGNESIUM, CADMINUM AND THE ALKALINE EARTH METALS, THE BALANCEPARTICULATED MAGNESIUM METAL, SAID COMBUSTIBLE MATERIAL HAVING THE FORMOF AN EXTRUD PREPARED BY DIE EXPRESSING SAID ADMIXTURE AT A TEMPERATUREIN THE RANGE OF 300 TO 850*F. WHEREBY THE MAGNESIUM METAL PARTICLESUNDEGO A WELDING TOGETHER DURING DIE EXPRESSION, BUT BELOW THETEMPERATURE AT WHICH THE SUB STANCE FROM A FLUID, THEREBY TO AVOIDDRIPPING MOLTEN METAL DURING COMBUSTION.